5o6 



Journal of Agricultural Research 



Vol. ni. No. 6 



All of the 13 plates exposed previous to this time yielded colonies of 

 Endothia parasitica. Eight of these exposures were made in the open 

 field at varying distances south and west of the plot of diseased trees (fig. 

 2), the wind being from the northeast. The distance relations brought 

 out by these tests are discussed later. Although five ascospore traps 

 showed evidences of the occurrence of spore expulsion after 10.07 a. m., 

 no colonies of this fungus appeared in any of the plates exposed after 

 9.23 a. m. This indicates that spores were evidently not sufficiently 

 numerous in the air after that time to be detected by the exposure- 

 plate method. 



The results obtained on September 21, as shown in Tables II and VI, 

 bring out again the direct relation of rain to wind dissemination. Two 

 plates exposed during a i6-minute interval between showers in the 

 early morning yielded colonies of Endothia parasitica in such numbers as 

 to prove without doubt that ascospores were very prevalent in the air at 

 that time. After the second rain, ending at 8.20 a. m., only the five 

 plates exposed within an hour after its cessation yielded colonies of E. 

 parasitica, even though 14 out of the 21 ascospore traps examined showed 

 that considerable spore expulsion had taken place after 10 a. m. (Table 

 XI). However, a south wind of increasing velocity prevailed, and at 9.2 1 

 the sun appeared, causing a marked rise in temperature, so that the bark 

 dried very rapidly after that time. Furthermore, the higher wind may 

 also have dispersed and scattered the fewer spores expelled thereafter to 

 such an extent that none happened to fall into the exposed plates. 



Table VI, — Record of exposure plates viadc on September zi, IQIJ, at West Chester, Pa. 



RAIX XO. I (about 0.35 INCH. CEASED 6.24 A. M.) 



RAIN NO. 2 (ABOUT o.oS INCH, 6.40 TO 8.20 A. M.) 



5071 

 5072 



5073 

 5074 

 5075 

 5076 



5077 

 5078 

 5079 

 5080 

 5081 

 5082 



5083 

 5084 



8.35 a.m. 



8.37 a. m . 

 9.04 a. m . 

 9.16 a. m . 

 9.21 a m. 

 9.40 a. m. 

 9.43 a. m. 

 10.25 a. tn 

 10.28 a. in 

 10.46 a m 

 11.00 a. tn 

 11.07 ^- ™ 

 11.48 a m 

 1.19 p. m . 



62 



24 

 19 



I 



o Numerous. 



6 Few. 



